Light emitting device and method of manufacturing the same

ABSTRACT

A light emitting device is disclosed. The light emitting device includes a conductive support layer; a reflective layer disposed on the conductive support layer; a nitride semiconductor layer disposed on the reflective layer. Furthermore, the nitride semiconductor layer includes a second-type semiconductor layer on the reflective layer, an active layer on the second-type semiconductor layer, and a first-type semiconductor layer on the active layer; a light extraction structure disposed on the first-type semiconductor layer; and a first-type electrode disposed on the light extraction structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of co-pending U.S. patent applicationSer. No. 14/147,947 filed Jan. 6, 2014, which is a continuation of U.S.patent application Ser. No. 13/489,158 (now U.S. Pat. No. 8,643,035,issued Feb. 4, 2014), filed Jun. 5, 2012, which is a continuation ofU.S. patent application Ser. No. 12/731,029 (now U.S. Pat. No.8,598,607, issued Dec. 3, 2013), filed Mar. 24, 2010, which is aContinuation application of U.S. patent application Ser. No. 11/707,167(now U.S. Pat. No. 7,714,337, issued May 11, 2010), filed Feb. 16, 2007,which claims the priority benefit of Korean Patent Application No.10-2006-0021443, filed on Mar. 7, 2006. The entire contents of all ofthe above applications are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light emitting device and a method ofmanufacturing the same, and more particularly, to a light emitting diodehaving a plurality of nanocones formed at the surface thereof byepitaxial growth, whereby the light extraction efficiency of the lightemitting diode is improved, and a method of manufacturing the same.

2. Discussion of the Related Art

Generally, a light emitting diode (LED) is a kind of semiconductordevice that converts electricity into light using the characteristics ofa compound semiconductor to transmit and receive a signal or is used asa light source. The light emitting diode generates high-efficiency lightat low voltage with the result of high energy saving efficiency.Recently, the brightness of the light emitting diode, which was alimitation of the light emitting diode, has considerably improved, andtherefore, the light emitting diode has been widely used throughoutindustry, such as backlight units, electric bulletin boards, displayunits, electric home appliances, and various kinds of automatedequipment. Especially, a nitride light emitting diode has attractedconsiderable attention in the environmentally-friendly aspect becausethe energy band gap of an active layer constituting the nitride lightemitting diode is wide with the result that light emitting spectrum isformed widely from ultraviolet rays to infrared rays, and the nitridelight emitting diode does not contain environmentally hazardousmaterials, such as arsenic (As) and mercury (Hg).

In addition, research is being carried out on a light emitting diodehaving high brightness that is applicable in various applications. Forexample, a light emitting diode having high brightness may be obtainedby improving the quality of an active layer of the light emitting diodeto increase inner quantum efficiency or by assisting light generatedfrom the active layer to be discharged to the outside and collecting thelight in a desired direction to increase light extraction efficiency.Although attempts are being currently made to increase both the innerquantum efficiency and the light extraction efficiency, more activeresearch is being carried out on a method of improving the electrodedesign, the shape, and the package of the light emitting diode toincrease the light extraction efficiency than a method of improving thequality of a semiconductor material to increase the inner quantumefficiency.

Up to now, a method of increasing the transmissivity of an upperelectrode of the light emitting diode or a method of disposing areflection plate at the outside of the light emitting diode to gatherlight discharged to a sapphire substrate of the light emitting diode orthe side of the light emitting diode upward has been mainly attempted.The light extraction efficiency is decided by the ratio of electronsinjected into the light emitting diode to photons discharged from thelight emitting diode. As the light extraction efficiency is increased,the brightness of the light emitting diode is increased. The lightextraction efficiency of the light emitting diode is greatly affected bythe shape or the surface state of a chip, the structure of the chip, andthe package form of the chip. Consequently, it is necessary to paycareful attention when designing the light emitting diode.

For a light emitting diode with high output and high brightness, thelight extraction efficiency acts as an important factor to decide thelight emission efficiency of the light emitting diode. In a conventionalmethod of manufacturing a nitride light emitting diode, however, thelight extraction efficiency is limited.

FIG. 1 is a sectional view illustrating a conventional nitride lightemitting diode. As shown in FIG. 1, the conventional nitride lightemitting diode is constructed in a structure in which a buffer layer 11,an n-type nitride semiconductor layer 12, an active layer 13, and ap-type nitride semiconductor layer 14 are sequentially stacked on asapphire substrate 10. Mesa etching is carried out from the p-typenitride semiconductor layer 14 to a portion of the n-type nitridesemiconductor layer 12. As a result, the etched portion of the n-typenitride semiconductor layer 12 is exposed to the outside. An n-electrode15 is formed on the exposed portion of the n-type nitride semiconductorlayer 12. Also, a transparent electrode 16 is formed on the p-typenitride semiconductor layer 14, and a p-electrode 17 is formed on thetransparent electrode 16.

A method of manufacturing the nitride light emitting diode is carriedout as follows. First, a buffer layer 11, an n-type nitridesemiconductor layer 12, an active layer 13, and a p-type nitridesemiconductor layer 14 are sequentially formed on a sapphire substrate10. Subsequently, mesa etching is carried out from the p-type nitridesemiconductor layer 14 to a portion of the n-type nitride semiconductorlayer 12 using a reactive ion etching (RIE) method. A transparentelectrode 16 to improve the ohmic characteristics is formed on thep-type nitride semiconductor layer 14, and a p-electrode 17 is formed onthe transparent electrode 16. Subsequently, an n-electrode 15 is formedon the mesa etched and thus exposed portion of the n-type nitridesemiconductor layer.

The light emitting diode is driven as follows. When voltage is appliedto the p-electrode 17 and the n-electrode 15, holes and electrons movefrom the p-type nitride semiconductor layer 14 and the n-type nitridesemiconductor layer 12 to the active layer 13. The electrons and theholes are recoupled with each other in the active layer 13, wherebylight is generated from the active layer 13. The light generated fromthe active layer 13 advances upward and downward from the active layer13. The upward-advancing light is discharged to the outside through thetransparent electrode 16 thinly formed on the p-type nitridesemiconductor layer 14. On the other hand, the downward-advancing lightis discharged downward through the substrate 10, and is then absorbedinto solder used when packaging the light emitting diode, or else, thedownward-advancing light is reflected by the substrate 10, moves upward,and is then reabsorbed into the active layer 13, or is discharged to theoutside through the transparent electrode 16.

In the conventional nitride light emitting diode, however, a totalreflection condition occurs due to the difference in a refractive indexbetween a nitride semiconductor material and the outside when lightgenerated from the active layer is discharged to the outside. As aresult, light incident at an angle greater than the critical angle ofthe total reflection is not discharged to the outside but is reflectedinto the light emitting diode. Specifically, as shown in FIG. 2, whenlight generated from an active layer 30 reaches the surface of a nitridesemiconductor material 40, the light is not discharged to the outsidebut is reflected into the light emitting diode if the incident angle ofthe incident light exceeds the critical angle θ_(c), which is decided bythe outer refractive index and the refractive index of the nitridesemiconductor material. The reflected light is diminished as the lightpasses through several channels.

The critical angle is decided by Snell's Law. Specifically, the criticalangle may be obtained by the following equation.

sin θ_(c) =N ₁ /N ₂  [Equation 1]

Where, θ_(c) is the critical angle, N₁ is the outer refractive index ofthe light emitting diode, and N₂ is the inner refractive index of thelight emitting diode.

When the light generated from the active layer reaches the surface ofthe nitride semiconductor material as described above, the light istotally reflected into the light emitting diode and thus diminished,whereby the light extraction efficiency of the conventional nitridelight emitting diode is lowered.

In order to solve the above-mentioned problem, there has been proposed amethod of etching the surface of the light emitting diode to rough thesurface of the light emitting diode. However, the etching process isfurther performed after the growth of the thin film on the lightemitting diode, whereby the method of manufacturing the light emittingdiode is complicated, and therefore, the time necessary formanufacturing the light emitting diode is increased. In addition, aconventional light emitting device package structure is manufactured byplastic injection molding, and therefore, the miniaturization and thinshaping possibilities of the light emitting device package structure arelimited. Consequently, the conventional light emitting device packagestructure is not suitable for a current tendency requiring the reductionin weight and size of electronic products.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a light emittingdevice and a method of manufacturing the same that substantially obviateone or more problems due to limitations and disadvantages of the relatedart.

An object of the present invention is to provide a light emitting devicewherein a plurality of nanocones are grown simultaneously at the step ofgrowing a thin nitride film, whereby the surface of the light emittingdevice has surface roughness without an additional etching process and amethod of manufacturing the same.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, alight emitting device includes a buffer layer formed on a substrate, anitride semiconductor layer including a first semiconductor layer, anactive layer, and a second semiconductor layer, which are sequentiallystacked on the buffer layer, a portion of the first semiconductor layerbeing exposed to the outside by performing mesa etching from the secondsemiconductor layer to the portion of the first semiconductor layer, andat least one nanocone formed on the second semiconductor layer.

In another aspect of the present invention, a method of manufacturing alight emitting device includes sequentially forming a buffer layer and anitride semiconductor layer including a first semiconductor layer, anactive layer, and a second semiconductor layer on a substrate,performing mesh etching from the second semiconductor layer to a portionof the first semiconductor layer to expose the portion of the firstsemiconductor layer to the outside, and forming a plurality of nanoconeson the second semiconductor layer.

In another aspect of the present invention, a light emitting deviceincludes an ohmic layer formed on a conductive support film, a nitridesemiconductor layer formed on the ohmic layer, the nitride semiconductorlayer including a second semiconductor layer, an active layer, and afirst semiconductor layer, and at least one nanocone formed on the firstsemiconductor layer.

In a further aspect of the present invention, a method of manufacturinga light emitting device includes sequentially forming a nitridesemiconductor layer including a first semiconductor layer, an activelayer, and a second semiconductor layer on a substrate, and removing thesubstrate and forming a plurality of nanocones on the firstsemiconductor layer.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWING

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a sectional view illustrating a conventional nitride lightemitting diode;

FIG. 2 is a view illustrating a principle in which light generated froman active layer of a conventional light emitting device is totallyreflected from a nitride semiconductor surface;

FIG. 3 is a graph illustrating the relationship between growth time andgrowth temperature in a nanocones growth method according to the presentinvention;

FIGS. 4A to 4D are sectional views illustrating a first embodiment oflight emitting device according to the present invention and a method ofmanufacturing the same;

FIGS. 5A to 5E are sectional views illustrating a second embodiment oflight emitting device according to the present invention and a method ofmanufacturing the same; and

FIG. 6 is a scanning electron microscope (SEM) photograph illustratingnanocones according to the present invention.

DETAILED DESCRIPTION OP THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

A light emitting device according to the present invention ischaracterized in that nanocones are formed on a nitride semiconductorlayer. Consequently, when light generated from an active layer reachesthe surface of the light emitting device, the amount of light totallyreflected into the light emitting device and thus diminished is reduced,whereby the light extraction efficiency of the light emitting device isimproved.

FIG. 3 is a graph illustrating the relationship between growth time andgrowth temperature in a nanocones growth method according to the presentinvention.

First, as shown in FIG. 3, a sapphire substrate is heat-treated at atemperature of 1100° C. for 10 minutes in a hydrogen atmosphere toremove an oxide film from the surface of the sapphire substrate. Next,an ammonia (NH₃) gas is injected to nitridate the sapphire substrate.Subsequently, the interior temperature (growth temperature) of thegrowth chamber is lowered to a temperature of 500° C., and alow-temperature GaN buffer layer is grown. Generally, there does notexist a substrate identical in a lattice constant and a coefficient ofthermal expansion to a nitride semiconductor material, such as GaN. Forthis reason, a nitride semiconductor material, such as GaN, is normallygrown on the sapphire substrate. At this time, a buffer layer havingsmall thickness is formed at low temperature to reduce the difference inthe lattice constant and the coefficient of thermal expansion betweenthe sapphire substrate and the nitride semiconductor material grown onthe sapphire substrate and thus to prevent deterioration of thecrystallinity.

The low-temperature buffer layer may be grown using metal organicchemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). Asthe low-temperature buffer layer may be used a material having a formulaof Al_(x)In_(y)Ga_((1-x-y))N (where, 0≦x≦1, 0≦y≦1, and 0≦x+y≦1) as wellas the GaN layer. Preferably, the growth temperature of thelow-temperature buffer layer is between 500 and 600° C.

Subsequently, the interior temperature of the growth chamber is raisedto a temperature of 900 to 1100° C. (1060° C. in this embodiment), andthen a thin nitride film having a formula of Al_(x)In_(y)Ga_((1-x-y))N(where, 0≦x≦1, 0≦y≦1, and 0≦x+y≦1) is grown for 60 minutes or more. Atthis time, it is more preferable to grow the thin nitride film afterheat-treating the buffer layer for several minutes rather than todirectly grow the thin nitride film at a temperature of 1060° C. Whenthe GaN buffer layer is grown on the sapphire substrate at lowtemperature, a GaN crystal is primarily grown into the shape of anuneven column. A crystal grown at high temperature based on the GaNcrystal starts to be grown evenly to the side. After the crystal isgrown to a specific thickness, the crystal growth of a relatively evensingle crystal is possible.

When the thin nitride film having the formula ofAl_(x)In_(y)Ga_((1-x-y))N (where, 0≦x≦1, 0≦y≦1, and 0≦x+y≦1) is grown onthe above-described buffer layer, tri-methyl-aluminum (TMAl) ortri-ethyl-aluminum (TEAl) is used as an Al source, tri-methyl-indium(TMIn) or tri-ethyl-indium (TEIn) is used as an In source, andtri-methyl-gallium (TMGa) or tri-ethyl-gallium (TEGa) is used as a Gasource. In addition, a NH₃ or N₂ gas is used as an N source, and ahydrogen (H₂) gas is used as a carrier gas to carry Al, In and Gasources. When a thin GaN film is grown, for example, tri-methyl-gallium(TMGa) and NH₃ gases, which are reaction precursors, are injected into areactor at a speed of 1 to 50 sccm and 1000 to 2000 sccm, respectively,using a hydrogen gas, and then the materials are chemically reacted witheach other at the top of the buffer layer to grow the thin GaN film.

At this time, it is preferable for the hydrogen gas, which is a carriergas, to have an amount of 1500 to 3000 sccm. For a p-type thin GaN film,bis(cyclopentyl)magnesium ((C₅H₅)₂Mg) is injected into the reactor todeposit a magnesium-doped thin GaN film, which is heat-treated such thatthe magnesium-doped thin GaN film is activated, whereby the p-type thinGaN film is grown. For an n-type thin GaN film, on the other hand,silane (SiH₄) is injected into the reactor to deposit a silicon-dopedthin GaN film, which is heat-treated such that the magnesium-doped thinGaN film is activated, whereby the n-type thin GaN film is grown. At thestep of growing the thin nitride film, an n-type nitride semiconductorlayer, an active layer, and a p-type nitride semiconductor layer may besequentially stacked on the low-temperature buffer layer to form a lightemitting structure.

Subsequently, the interior temperature of the growth chamber is loweredto a temperature of 400 to 900° C., and then a plurality of nanoconesare grown on the thin nitride film for 10 to 40 minutes. At this time,tri-methyl-gallium (TMGa) and NH₃ gases, which are reaction precursors,are injected into the reactor at a speed of 1 to 50 sccm and 100 to 1000sccm, respectively, using a hydrogen gas. Also, the amount of thehydrogen gas, which is a carrier gas, is reduced to a half or more, andthe hydrogen gas is injected into the reactor at a speed of 300 to 1000sccm to grow a plurality of nanocones on the thin nitride film.Preferably, the nanocones have a size of 10 nm to 1000 nm. When thenanocones are grown, the growth temperature is lowered, and the flowrate of the NH₃ gas is reduced as compared to when the thin nitride filmis grown, whereby the nanocones are formed in the shape of a pyramid.

That is, the growth temperature is lowered, and the flow rate of the NH₃gas is reduced such that the vertical growth is superior to thehorizontal growth, whereby the nanocones are grown. In this case, theflow rate of the NH₃ gas corresponds to approximately ⅓ to ½ that of thegas when the thin nitride film is grown.

FIGS. 4A to 4D are sectional views schematically illustrating a firstembodiment of light emitting device according to the present inventionand a method of manufacturing the same.

First, a buffer layer 110, an n-type nitride semiconductor layer 120, anactive layer 130, and a p-type nitride semiconductor layer 140 aresequentially stacked on a substrate 100 (see FIG. 4A). The substrate 100may be a sapphire (Al₂O₃) substrate, a silicon carbide (SiC) substrate,a silicon (Si) substrate, a gallium arsenide (GaAs) substrate, or aquartz substrate. Among them, the sapphire substrate is preferably usedas the substrate 100 according to the present invention. The bufferlayer 110 serves to eliminate the lattice mismatch between the substrate100 and a nitride semiconductor material and the difference in acoefficient of thermal expansion between the substrate 100 and thenitride semiconductor material. A low-temperature growth GaN or AlNlayer is used as the buffer layer 110.

The n-type nitride semiconductor layer 120 is made of an n-dopedsemiconductor material having a formula of Al_(x)In_(y)Ga_((1-x-y))N(where, 0≦x≦1, 0≦y≦1, and 0≦x+y≦1). Preferably, the n-type nitridesemiconductor layer 120 is made of n-GaN. The active layer 130 has amulti-quantum well (MQW) structure. The active layer 130 may be made ofGaN or InGaN. Also, the p-type nitride semiconductor layer 140 is madeof a nitride semiconductor material having a formula ofAl_(x)In_(y)Ga_((1-x-y))N (where, 0≦x≦1, 0≦y≦1, and 0≦x+y≦1), like then-type nitride semiconductor layer 120. The nitride semiconductormaterial is p-doped. The buffer layer 110, the n-type nitridesemiconductor layer 120, the active layer 130, and the p-type nitridesemiconductor layer 140 formed on the substrate 100 may be grown usingvapor deposition, such as metal organic chemical vapor deposition(MOCVD), molecular beam epitaxy (MBE), or hydride vapor phase epitaxy(HVPE).

The n-type nitride semiconductor layer 120, the active layer 130, andthe p-type nitride semiconductor layer 140 are grown at a temperature of700 to 1100° C.

Subsequently, mesa etching is carried out from the p-type nitridesemiconductor layer 140 to a portion of the n-type nitride semiconductorlayer 120 such that the etched portion of the n-type nitridesemiconductor layer 120 is exposed to the upside (see FIG. 4B). When aninsulative substrate, such as the sapphire substrate, is used as thesubstrate 100, it is not possible to form an electrode at the bottom ofthe substrate 100. Consequently, the mesa etching is carried out fromthe p-type nitride semiconductor layer 140 to a portion of the n-typenitride semiconductor layer 120 so as to secure a space necessary toform the electrode. After the mesa etching is carried out, a process forforming a transparent electrode on the p-type nitride semiconductorlayer 140 may be further performed. The p-type nitride semiconductorlayer 140 has low dopant concentration. As a result, the contactresistance of the p-type nitride semiconductor layer 140 is high, andtherefore, the p-type nitride semiconductor layer 140 has a poor ohmiccharacteristic. In order to improve the ohmic characteristic of thep-type nitride semiconductor layer 140, therefore, the transparentelectrode is formed on the p-type nitride semiconductor layer 140. Thetransparent electrode may be constructed in a dual-layered structureincluding nickel (Ni) and gold (Au). Alternatively, the transparentelectrode may be made of indium tin oxide (ITO). The transparentelectrode forms an ohmic contact, while increasing the current injectionarea, to decrease forward voltage V_(f).

Subsequently, a plurality of nanocones 150 are grown on the p-typenitride semiconductor layer 140 (see FIG. 4C). The nanocones 150 aregrown at low temperature, i.e., at a temperature of 400 to 900° C.,preferably 600 to 800° C., using metal organic chemical vapor deposition(MOCVD). The nanocones 150 are made of a nitride semiconductor materialhaving a formula of Al_(x)In_(y)Ga_((1-x-y))N (where, 0≦x≦1, 0≦y≦1, and0≦x+y≦1). Preferably, the nanocones 150 have a size of 10 nm to 1000 nm.Unlike the n-type nitride semiconductor layer 120, the active layer 130,and the p-type nitride semiconductor layer 140, the nanocones 150 aregrown at low temperature, i.e., at a temperature of 400 to 900° C., andlow flow rate of the NH₃ gas.

As described above, the plurality of nanocones 150 are formed on thep-type nitride semiconductor layer 140 by controlling the temperatureand the flow rate of the NH₃ gas. Specifically, when the nanocones 150are grown, a ratio of the horizontal growth to the vertical growth iscontrolled to form the nanocones 150 in the shape of a pyramid. Thecontrollable parameters are the growth temperature and the flow rate ofthe NH₃ gas. When the growth temperature is raised, and the flow rate ofthe NH₃ gas is increased, the horizontal growth is increased. When thegrowth temperature is lowered, and the flow rate of the NH₃ gas isdecreased, on the other hand, the vertical growth is increased. It isalso possible to form the nanocones 150 into various desired shapes bycontrolling the growth parameters as described above.

Subsequently, the nanocones 150 are partially removed, a p-electrode 160is formed on a portion of the p-type nitride semiconductor layer 140where the nanocones 150 are removed, and an n-electrode 170 is formed onthe exposed portion of the n-type nitride semiconductor layer 120 (seeFIG. 4D). The p-electrode 160 may be formed on the nanocones 150. Thep-electrode 160 and the n-electrode 170 are made of any one selectedfrom a group consisting of chrome (Cr), nickel (Ni), gold (Au), aluminum(Al), titanium (Ti), and platinum (Pt), or an alloy thereof.

In the first embodiment of light emitting device according to thepresent invention and the method of manufacturing the same, theplurality of nanocones are grown simultaneously at the step of growingthe thin nitride film. Consequently, the surface of the light emittingdevice has surface roughness without an additional etching process,whereby the manufacturing process is simplified, and therefore, the timenecessary for manufacturing the light emitting diode is reduced.

FIGS. 5A to 5E are sectional views schematically illustrating a secondembodiment of light emitting device according to the present inventionand a method of manufacturing the same.

First, an n-type nitride semiconductor layer 210, an active layer 220,and a p-type nitride semiconductor layer 230 are sequentially stacked ona substrate 200 (see FIG. 5A). Subsequently, an ohmic layer 240 and aconductive support film 250 are sequentially formed on the p-typenitride semiconductor layer 230 (see FIG. 5B). The ohmic layer 240 ismade of a thin metal film including nickel (Ni) and gold (Au). The thinmetal film mainly including nickel (Ni) is heat-treated in an oxygenatmosphere to form an ohmic contact having a specific contact resistanceof approximately 10⁻³ to 10⁻⁴ Ωcm². When the thin metal film includingnickel (Ni) and gold (Au) is used as the ohmic layer 240, thereflexibility of the ohmic layer 240 is highly increased, and therefore,it is possible for the ohmic layer 240 to effectively reflect lightemitted from the active layer 220. Consequently, it is possible toobtain a reflecting effect without the formation of an additionreflector.

The conductive support film 250 serves as a p-electrode. Consequently,it is preferable to form the conductive support film 250 using metalhaving high electrical conductivity. In addition, it is required for theconductive support film 250 to sufficiently diffuse heat generatedduring the operation of the light emitting device. Consequently, it ispreferable to form the conductive support film 250 using metal havinghigh thermal conductivity. Furthermore, in order to separate a waferinto a plurality of individual chips through a scribing process and abreaking process while the entire wafer is not bent during the formationof the conductive support film 250, it is required for the conductivesupport film 250 to have mechanical strength to some extent.Consequently, it is preferable to form the conductive support film 250using an alloy of soft metal having high thermal conductivity, such asgold (Au), copper (Cu), silver (Ag), and aluminum (Al) and hard metalwhich has a crystal structure and a crystal lattice constant similar tothose of the above-specified soft metal to minimize the occurrence ofinternal stress when the alloy is made and has high mechanical strength,such as nickel (Ni), cobalt (Co), platinum (Pt), and palladium (Pd).

Subsequently, the substrate 200 is removed from the n-type nitridesemiconductor layer 210 (see FIG. 5C). The removal of the substrate 200may be carried out by a laser lift off (LLO) method using excimer laseror a dry-type and wet-type etching method. Preferably, the removal ofthe substrate 200 is carried out by the laser lift off (LLO) method.Specifically, when excimer laser light having a specific wavelengthrange is focused and irradiated on the substrate 200, thermal energy isconcentrated on the interface between the substrate 200 and the n-typenitride semiconductor layer 210. As a result, gallium and nitrogenmolecules are separated from each other at the surface of the n-typenitride semiconductor layer 210, and therefore, the substrate 200 isinstantaneously separated from the n-type nitride semiconductor layer210 at the position where the laser light is transmitted.

Subsequently, a plurality of nanocones 260 are grown on the p-typenitride semiconductor layer 210 (see FIG. 5D). The nanocones 260 aregrown at low temperature, i.e., at a temperature of 400 to 900° C.,preferably 600 to 800° C., using metal organic chemical vapor deposition(MOCVD). The nanocones 260 are made of a nitride semiconductor materialhaving a formula of Al_(x)In_(y)Ga_((1-x-y))N (where, 0≦x≦1, 0≦y≦1, and0≦x+y≦1). Preferably, the nanocones 260 have a size of 10 nm to 1000 nm.Unlike the n-type nitride semiconductor layer 210, the active layer 220,and the p-type nitride semiconductor layer 230, the nanocones 150 aregrown at low temperature, i.e., at a temperature of 400 to 900° C., andlow flow rate of the NH₃ gas.

Subsequently, the nanocones 260 are partially removed, an n-electrode270 is formed on a portion of the p-type nitride semiconductor layer 210where the nanocones 260 are removed (see FIG. 5E). Meanwhile, then-electrode 160 may be formed on the nanocones 260 as in the firstembodiment of light emitting device and the method of manufacturing thesame.

FIG. 6 is a scanning electron microscope (SEM) photograph illustratingnanocones according to the present invention.

As shown in FIG. 6, a plurality of nanocones are formed at the surfaceof a light emitting diode. Consequently, when light generated from anactive layer reaches the surface of the light emitting diode, the amountof light totally reflected into the light emitting device and thusdiminished is reduced.

As apparent from the above description, the present invention ischaracterized in that a plurality of nanocones are grown simultaneouslyat the step of growing a thin nitride film, whereby the surface of alight emitting device has surface roughness without an additionaletching process. Consequently, the manufacturing process is simplified,and therefore, the time necessary for manufacturing the light emittingdevice is reduced.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A light emitting device, comprising: a conductivesupport layer; a reflective layer disposed on the conductive supportlayer; a nitride semiconductor layer disposed on the reflective layer,wherein the nitride semiconductor layer includes a second-typesemiconductor layer on the reflective layer, an active layer on thesecond-type semiconductor layer, and a first-type semiconductor layer onthe active layer; a light extraction structure disposed on thefirst-type semiconductor layer; and a first-type electrode disposed onthe light extraction structure.
 2. The light emitting device of claim 1,wherein the light extraction structure includes a plurality of cones. 3.The light emitting device of claim 2, wherein a top of any of the conesis higher than a middle between a top surface of the first-typeelectrode and a bottom surface of the first-type electrode, on a topsurface of the first-type semiconductor layer.
 4. The light emittingdevice of claim 1, wherein the conductive support layer includes a softmetal and a hard metal.
 5. The light emitting device of claim 4, whereinthe soft metal includes Au, Cu, Ag, and Al.
 6. The light emitting deviceof claim 4, wherein the hard metal includes Ni, Co, Pt, and Pd.
 7. Thelight emitting device of claim 1, wherein the reflective layer includesa metal.
 8. The light emitting device of claim 7, wherein the metalincludes Ni and Au.
 9. The light emitting device of claim 1, wherein thereflective layer has a specific contact resistance of 10-3 Ωcm2 to 10-4Ωcm2.
 10. The light emitting device of claim 2, wherein the cones aredisposed under and beside the first-type electrode.
 11. The lightemitting device of claim 2, wherein at least one of the cones is a nanoscale cone.
 12. The light emitting device of claim 11, wherein the nanoscale cone has a size of 10 nm to 1000 nm.
 13. The light emitting deviceof claim 2, wherein the cones are made of a nitride semiconductormaterial.
 14. The light emitting device of claim 13, wherein the nitridesemiconductor material of the cones has a formula of AlxInyGa(1-x-y)N(where, 0≦x≦1, 0≦y≦1, and 0≦x+y≦1)
 15. The light emitting device ofclaim 2, wherein the at least one of the cones is formed with a shape ofa pyramid.
 16. The light emitting device of claim 1, wherein the activelayer includes InGaN, and at least one of the first-type semiconductorlayer or the second-type semiconductor layer includes AlGaN.
 17. Thelight emitting device of claim 1, wherein the light extraction structureincludes substantially the same material as that of the nitridesemiconductor layer.
 18. The light emitting device of claim 1, whereinthe light extraction structure is a part of the nitride semiconductorlayer.
 19. The light emitting device of claim 2, wherein the cones donot overlap each other.
 20. The light emitting device of claim 1,wherein the light extraction structure is disposed on an entire uppersurface of the first-type semiconductor layer.